Apparatus for assembling centrifugal impellers



7 June 1946- A. J. PHELAN ET AL 2,402,204-

APPARATUS FOR ASSEMBLiNG CENTRIFUGAL IMPELLERS Filed Nov. 19, 1941 2Sheets-Shet 1 jig. 1

IN V EN TORS ARTHUR J. PHELAN. Y VLADIMIR H. MVLECKA.

A T TORNE YS.

June 18, 1946. A. J. PHELAN ET AL 2,402,294

APPARATUS FOR ASSEMBLING CENTRIFUGAL IMPELLERS Filed Nov. 19, 1941 2Sheets-Shea t 2 Ez'g. 5. 77

66 a: a; 65" las IN VEN TORS ARTHUR J. PHELAN. Y VLADIMIR H. PAVLECKA.

ATTOPNEYS.

method, within the scope of the appended clain a.

Patented June 1 8, 1946 APPARATUS FOR AsssMsLmG CENTRIFUGAL IMPELLERSArthur J. Phelan and Vladimir H. Pavlecka, Pacific Palisades, Call!asslgnors to Northrop Aircraft, Inc, Hawthorne, Calm, a corporatlon ofCalifornia Application November 19, 1941, Serial No. 4193252 4 Claims.(Cl. 113-59) bustion turbine shown, described and claimed in.

the following prior filed applications:

Serial Name Title No Filed Povlecko Gas $lll'blH6. 483,338 July 21,1941Pavlecko and Northrop- (lompressorflm 413,731 Oct. 6.1941 Do Airplanepower 418,475 Nov. 10.1941

plfill Among the objects of our invention are: To provide a light,strong and integral centrtiusol impeller; to provide a means and methodoi es= sembling a centrifugal impeller; to provide a means and method offorming a oentr ugal lrnpeller by copper brazing in a hydrogenatmosphere; to provide a complement of fixtures whereby a centrifugalimpeller may be assembled by copper brazing, without the use of belts orsimilar materials; to provide a anal method of assembling a rotor disc,centrifugal vanes and a cover into a unitary iinneller sttuc ture bybrazing; to provide a centrifugal impeller having clean, smooth andfully con tours and air passages, and to provide a simple, efficient andlight-weight centrifugal adapted for high speed operation.

0m invention possesses'numerous other jects and features of advantage,some of will It, together with the foregoing, will be teeth in notes thefollowing description of specific embodying and utilizing our noveltherefore to be understood that our met applicable to other apparatus,and we no not limit ourselves, in any way, to the an, ratus of thepresent application, as we may adopt various other apparatusembodiments, utilising in the prior applications cited above, gascombustion turbine is disclosed wherein two centrifugal impellers areutilized in series to Zero vide the supply of compressed sit for thecombustion. Inasmuch as the preferable use to": such a turbine is forthe propulsion of sli crait, it is essential that the impellers in thecompressor be of highest strength, of light-weight, be por fectlybalanced, and have clean air passages to obtain maximum efllciencyoBroadly as to method our invention comprises the assembly of centrifugalvanes on a rotor disc with the application of a cover to the vanes, thedisc, vanes and cover being brazed into a single unit by the use ofcopper in a hydrogen furnace, this brazing being accomplished underpressure. Preferably, the copper is interposed between mating surfacesin the form of a thin strip of exact size and position, so that afterthe brazing has taken place only an insignificant copper fillet ispresent at the junction of the mating surfaces. For certain work thisfillet may remain. For other work it can be removed for exceptionallyclean air channels.

The more detailed assembly steps comprise turning of a mating surface ona rotor ine'nber, together with the assembly the clad in turningfixture, followed by the turning of mating surfaces on the blades. Theblades placed in position on the, rotor disc tidh a thin copper striptherebetween, tools-crazed or taclnweldeci in posi 'lon. The opposite na edges of the vanes are the totaled to enact s by grinding, to avoiddisttsense of vanes clue to shock -loading thereof by intern st whichwould be encountered in e? A cover plate is then czuiulai'ly tL nod tomat:- with the exposed vane and con are applied to these cover plate isplaced nosi s that there will be a con vane edges and he me or rotozdisc, as the case The entire assembly droe'en furnace and a coltsthereto. The assembly is takes locs. The pressure the copper frombetween i and disc, to torn: an one: ture. -I'he insignificant t main insince for most omen pellet", or may be removed by ins oneration for mostetfici air giassages oi. the iinis lifter the vans; are the rotor disc,the cute? suriaces may then be machine finished. produces an impellerwherein all surfaces, terior and interior are machined, and where thevarious elements of the impellers are craze into a single nronerlydimensioned operating unit without the use oi bolts or similar tie mem'rs.

Broadly as to apparatus, our invention cor prises a. rotor disc having avane surface mechined thereon. Edges of a plurality of centrifusal vanesfit this surlace, and the vanes are held 1, .2 or posse of the in placeby tack-brazing or by tack-welding, with a thin strip of copper betweenthe vane edges and the mating surface on the disc. The opposite vaneedges fit a machined cover surface, and copper strips are applied to thevane surfaces by tack-brazing or tack-welding. The cover is then placedto the vanes, and the entire assembly is placed in a holding fixturepositioned within a hydrogen furnace until melting of the copper stripsoccurs.

While the assembly is in the hydrogen furnace, means are provided toapply pressure to the fixture so that as the copper melts, clearance aretaken up and the members forced into an exact fit. Upon cooling, therotor disc, the vanes and the cover are firmly brazed into a singleoperating unit, and, if desired, the small fillets formed at theedgesknay be removed to provide clean air channels.

Thus, we have provided an impeller wherein the interior is completelymachined.

In the drawings, which show one preferred embodiment of our invention:

Fig. 1 is a'vlew, partly in section and partly in elevation, of a rotordisc together with two impeller vanes drawn adjacent the positions theyare to occupy when Welded to the disc.

Fig. 2 me view, partly in section and partly in elevation, showing howthe impeller vanes are held in position on the rotor for tack-brazing orwelding.

Fig. 3 is a view, partly in section and partly in elevation, taken asindicated by the line 8-3 in i Fig. 2.

Fig. 4 is a view, partly in section and partly in elevation, taken asindicated by the line 5-45 in Fig. 3.

Fig. 5 is a view, partly in elevation and partly in section, showing theassembled impeller in po- 'sition in a hydrogen furnace ready for thebrazing operation.

Fig. 6 is a view, partly in elevation and partly in section, of thefinished impeller.

Fig. 7 is a view, partly in section and partly in elevation, of aportion of the impeller showing the copper strips in place.

Fig. 8 is a fragmentary view, partly in elevation and partly in section,showing a means of interlocking the blades with the impeller discs.

Fig. 9 is a sectional view taken as indicated by the line 9-9 in Fig. 8.

Referring directly to the drawings for a more detailed description ofour invention, beginning with Fig; 1 to show the sequence of operation:A rotor disc I is provided, having a central flange 2 and hollow hubs 3and 5 on opposite sides thereof. The hollow hub 5 is larger than hollowhub 3 and is positioned on the side of the rotor disc, to which impellervanes 6 are to be attached. The end of hub 5 is also provided with aninner shoulder I which is later to be threaded. Vanes tare curved as iswell known in the centrifugal compressor art, and comprise a curvedbasal portion I0 and an outwardly extending portion I I. Each blade alsohas a rotor edge 2, a cover edge I3, an angular entrance edge 94, and anexit edge I5. Disc i is also provided on its outer face with apositioning ridge I6. I

As a plurality of blades 6 are to be brazed to rotor disc I in equallyspaced positions around the rotor disc, the first step toward that endis to mount the rotor disc in a lathe and by simple annular machining toproduce vane face 26 to which the vanes 6 are to be brazed. The reof thecontours of the vane edges 52 with the rotor disc contour 20 may beobtained.

' The next stage in the assembly is the position- I ing on the machinedsurface 28 of the rotor disc i, of a plurality of sheet copper strips2i, these strips being cut to be thewidth and length of vane edges I2,which are to be brazed to surface 2!! of rotor I. These copper strips ZIare preferably about .010 thick and are tack-brazed to the surface 28 ofdisc 8 in the proper circumferential positions, one strip for each bladeto be mounted on surface 28. Opposite edges I3 of vanes 6 are not atthis time machined to final finish, but are provided with excess metalso that the final finish may take place after the vanes have beenfastened on the rotor disc.

Passing now to Figs. 2, 3, and 4 for a description of how the vanes 5are primarily held in ,place on the rotor disc, we have provided a basefixture 22 mounted on a foundation 23, on which rotor disc 8 may beplaced with vane surface 20 of this disc'facing upwardly. Positioningridgev It is used to prevent lateral motion of the disc on the fixture.

The full complement of vanes 6 is then mounted in a vane fixture 25.Vane fixture 25 is provided on the under surface thereof with an innerspacing ring 26, and an outer spacing ring 21,

these rings being provided with vane slots 28. 1

base pads 32 of sheet-lead are applied between fixture 25 and angularvane edges It to force the vanes inwardly. j

Fixture 25 with its vanes is inverted over disc I, the fixture beingprovided with a drop rim 33 extending over the exterior edge of therotor I. Vane tip apertures 34 are provided adjacent end edge I5 of eachvane. Fixture 25 is continued upwardly around hub 5 on the outsidethereof, and vane base apertures 35 are provided on each side ofentrance edges id of each vane. Threads 38 are provided on shoulder l ofrotor hub 5 and an upward extension member 40 is 'screwed'into thesethreads. Fixture 25 terminates upwardly in a cylindrical portion M,sliding freely on ex-' tension Aid. Extension dd is provided with endthreads 32 and a nut Q3 is utilized to force fixture 25 against upperedges I3 and Id of vanes 6 and thereby force each vane B into intimatecontact with the copper strips 2I positioned between each vane and thesurface 2% of rotor disc I.

After this locking together of the parts in their proper position isaccomplished, the vanes 6 are,

tack-brazed, preferably in three places, to rotor I. This isaccomplished by inserting the brazing torch for example, throughopenings 36 and brazing each vane to the rotor I at an entrance edgespot 65. The brazing torch is then inserted further into this opening36, and the vane is brazed to rotor I at a curvature spot 58. Thebrazing quired number of vanes 6 are then mounted in "is torch is alsoinserted through end openings 34 and the vane brazed to the rotor I at avane end spot 41.

Thus each vane at this time is securely held in position on the rotor Ialthough not in final posi tion, due to the thickness of the copperstrips 2i.

Fixture 25 and extension 48 may then be removed from the rotor disc Iand the rotor disc i removed from foundation member 22, carrying with itnow a full complement of impeller vanes 8.

The partially assembled impeller is then ready to. have the finishingoperation performed on edges it of the vanes to which edges an impellercover is to be brazed. This machining operation is performed preferablyby grinding in order to minimize disturbance ,of the vanes on the rotordisc, due to shock-loading which would be encountered by theintermittent cutting oil a lathe tool, in case annular turning of thevane edges were to be attempted. 'fiy grinding however, thisshock-loading may be entirely eliminated, and edges is of the vanes maybe readily finished to size and contour without disturbing thetackhrazlng or the vanes to the rotor.

After surfaces l3 of the vanes have been machined to their finisheddimensions while mounted on rotor I, the rotor and its tack-brazed vanesis provided with copper strips 49 required for the blazing of the edgesH to a cover 50.

These latter copper strips however, are not applied to cover 5B but areapplied directly to edges 13 of the vanes, and are tack-brazed in properposition thereon.

Cover 50 has a vane mating surface 5| whichhas been machined by annularturning to mate properly with the final finished dimensions and contourof edges 43 of the vanes, and this cover is then positioned on the vanes8, resting on the copper strips 49 that have been applied to edges 18 ofthe vanes. The assembled, but not yet brazed, impeller is then ready togo into a hydrogen furnace for the final brazing operation. Thishydrogen furnace will next be described, and is showninFig. 5.

A heavy base member 80 is provided supporting an overhead member 8! byupright bars 82. Mounted on base 50 is a metal pressure plate 84,preferably circular in plan form, carrying a layer of heat insulatingmaterial 65 on which is mounted an impeller support member 68 havin I anupper surface thereon roughly shaped to receive and properly support theouter surface of rotor disc I. It will be noted that shoulder i8 mayagain be utilized to properly position the impeller on the impellersupport 88. Pressure plate 64 and insulation 85 form part of the lowerwall of the oven, the remainder of the bottom of the oven, the sidewalls thereof, and most of the top being of conventional structure ofcircular plan form and comprising fire-brick 88, held together byproperly fire-resistant mortar 69, and enclosed by a thin metal cover70.

The top of the oven is provided with a central opening It through'whicha pressure cylinder 12 is freely movable, this pressure cylinder,however, being of heat insulating material and sufiiciently strong totransmit to the interior of the oven, hydraulic pressure through anexterior metal pressure fitting is from a hydraulic cylinder 74 by meansof a piston rod 15 operated in converttional manner by a piston 16within the cylinder 14, as is well known in the art. The cylinder issupplied with oil or the like from inlet 11.

The interior of the oven is provided with electrical heating elements 18of the proper capacity in hr-irm the interior" of the oven up to proper.it can at all times be told that the oven is receiving its fullcomplement of hydrogen gas.

The oven may be opened in any convenient manner, such as by end doors 80set in one end of the oven. The impeller rotor disc is placed on thesupport member 88, with the cover in place on the vanes. We prefer toinsert asbestos pads Bl between support 66 and the outer, now lower,face of rotor disc l. Similar asbestos pads 82 are placed between theouter, and in this position, upper surface of cover 50 and a clampingdome 83, which extends upwardly around hub 5 of the impeller rotor discto terminate in an upper surface 88 immediately below pressure cylinder752. We also prefer to provide asbestos pads 3'! between the dome 3'4and the angular entrance edges M of each vane so that the vanes will bemoved. inwardly by vertical pressure.

Thus the assembled but not yet brazed impeller is clamped between thebasal support memher it and the dome 84, with asbestos pads between theclamping members and the impeller structure. These asbestos pads areutilized to prevent any possibility of any brazing occurring between'themetal clamping members and the exterior surfaces of the assembledimpeller. Further, we prefer to form support member 88 and dome 84 ofhigh nickel-chromium heat resisting alloy ribbed and finned to providemaximum strength with the least weight in order to conserve heat.

The entire assembly of clamping members and impeller is then properlycentered in the oven beneath the hydraulic press arrangement, and thetop surface 86 of the dome is connected with pressure cylinder 72 of thehydraulic press by means of an asbestos cushion 90 and shims 8!, so thatthere will be no slack in the hydrauli drive.

The oven doors 8!! are then closed,,the hydrogen atmosphere fullyestablished, and the current to the heating element '55 is switched on.

Pressure is continuously applied to the elements of the rotor by the useof suitable liquid injection into cylinder M. As the temperaturegradually rises and as this temperatru'e approaches 2100 F., the copperstrips 2| and 69 melt and brazing is accomplished with the parts movedby the application of the hydraulic pressure into pressfit engagement,both radially and axially. The material selected for the impellerelement is preferably of steel such as SAE 4340 and therefore is notsubstantially affected by the heating to 2100" F.

As the copper melts, a perfect braze is accomplished and the tackingspots which have previously been made, merely melt into the finalbrazing. The copper which is between the vane edges and the impellerrotor and cover, is squeezed out as it melts to form a very slightfillet on each side of these edges, and the vanes come to rest, underpressure, with exact mating relationship of the machined edges of therotor and cover to which they are opposed. Thus the impeller after thefinal brazing has been accomplished is of exact dimensions. is brazedinto a complete asoaaoe unified structure, which can operate as a unitwithout the useof any bolts, rivets or equivalent tie members. Theinterior surfaces are entirely machined and the fillet caused by thecopper in the strips being forced outwardly, may easily be removed byrunning a small gouge or similar tool along the junction of the vanesand the rotor and cover, this tool being readily inserted from theperiphery fr the straight runs of the edges, and.

from the basal openings for the curved portions of the edges. After theimpeller is removed from the oven, as shown in Fig. 6, it can then bemounted in the lathe so that the exterior of the surfaces of the rotorand the cover may be machined into the desired final dimensions,including the removal of ridge it. 7

Thus we have provided a centrifugal impeller having clean machinedsurfaces throughout, both inside and outside the impeller. The impelleris formed solely by brazing without the use oi additional tie members.The impeller in this manms may be made very light in weight, exceedinglyaccurate as to dimensions, the air channels are clean, and the impellermay be perfectly bal-' I anced. The copper brazing provides" adequatestrength in use, particularly as temperatures even approaching thebrazing temperatures, are never encountered in the normal use of theimpeller. However it is to be noted that the melting temperature ofcopper is high, and for that reason impellers made as described hereincan be used inthe high pressure end of a compressor, as hasbeen'described in the applications cited above, even though the exit airtemperatures should rise, due to the air compression, to theneighborhood of 500-600 F.

It can be seen from, the above description of our method of copperbrazing "that the application' of external pressure, particularly anexternal pressure which is continued as the copper melts, provides acomplete, strong connection with exact mating of opposed surfaces.Hitherto, it has been thought feasible to copper-weld only parts held ina press-fit engagement prior to the application of the copper thereto.Nowhere, so

. far as we are aware, has copper brazing been practiced by theapplication of continuous external pressure to parts spaced by thincopper sheet. Hitherto, clamped pants have been copper brazed, but thismethod has not been found to be completely satisfactory, in that thepreload due to clamping almost invariably diminishes with temperature,due to heat sagging of the clamp. The pressure between parts thendiminishes, and the danger of misalinement' arises. Gravitationalclamping, using merely the weight ,of the parts, again has not proved tobe satisfactory, because misalinement may still arise and also becausethe pressure thus produced is not sumcient for successful brazing.However, by our method, Where hydraulic pressure is utilized,continuously operating. before, during, and after,

the melting of the copper strips, so that the parts are forced intoexact mating engagement as the copper strips melt, with all the partsheld completely in alinement, it can be seen that even though the partsbefore the brazing occurs are spaced, the forces acting on the parts a?such as to copper-weldthe parts with a press-fit engagement, with copperuniformly bonding the parts throughout the engaged surfaces.

In case rotational stresses are so great as to call for more thandependence on the copper alone for the joint between the vanes, disc 8,and cover 59, shear ribs Hill may be provided for ribs its fitting slotsml cut in the vane edges, as shown in Figs. 8 and 9. After brazing hasoccurred, the shear and other stresses are taken by the ribs as well asby the copper, and the vanes cannot straighten out even when rotated athigh speeds. V

We claim: 1. Apparatus for brazing a centrifugal impelle assemblyinvolving an impeller disc, a vane cover, vanes positioned between saiddisc and cover, copper strips between mating edges of said vanes andadjacent surfaces of said disc and cover, said apparatus comprising ahydrogen furnace wherein said disc, cover and vanes are positioned,means for heating said furnace, and positioning means for supportingsaid disc on the bottom of said furnace, and said second means comprisesa dome positioned over said cover and extending upwardly to terminateadjacent the top of said furnace, a movable heat insulating section'ofthe top of said furnace engaging the termination of said dome, and meansfor applying pressure to said section, said disc positioning means andsaid dome being of metaLwith non-metallic pads positioned between saidpositioning means and disc and between said dome and cover to preventbrazing therebetween, said dome having a surface exerting pressure onexposed portions of said vanes through additional non-metallic pads,said vares being curved with respect/t0 said disc and requiring aninwardly radial movement to mate ments for receiving said assembly withthe axisof said assembly vertical, a dome positioned to apply pressureto said cover, a movable insulating portion positioned to apply pressureto said dome, and a hydraulic cylinder having a piston connected to saidmovable insulating portion by a piston rod and pressure block.

3. Apparatus in accordance with claim 2 wherein said disc is supportedon a block and wherein an asbestos pad separates said block from saidlisc, and wherein an asbestos pad separates said cover from said dome,such apparatus including means for creating an atmosphere of a reducinggas around said assembly during heating.

4. Apparatus in accordance with claim 2 wherein said disc is supportedon a block and wherein an asbestos pad separates said block from saiddisc, wherein an asbestos pad separates said cover from said dome, andwherein said vanes are provided with curved basal portions and angularedges, said dome transmitting pressure to

